The lower the age of schoolchildren, the lower the risk of school-related uncontrollable infection clusters.
Evidence coming from retrospective and cross-sectional studies early in the pandemic [28-29] and from larger surveillance studies relating to the second peak of the pandemic, strongly supports minimal transmission rates in European day-care centres and primary schools, both for pupils and educational staff [30-32,42-44]. Significantly, this finding remains consistent also in areas of high COVID-19 background incidence and after systematic contact testing of each paediatric index case. Conversely, the only large outbreak of infection among younger children that has been reported in the literature is most likely explained by particular epidemiological features and does not provide conclusive counterevidence [33]. For older children and adolescents, larger or more numerous clusters of COVID-19 traced back to school environments have been evidenced, albeit very rarely, pointing to a potentially non-negligible transmissibility of Sars-CoV-2 in older age groups that could be explained by social as well as biological factors [13,34-35].